Synthesizing diamond under a static high-pressure must make use of catalysis of transition metal or transition alloy to actualize transform from graphite to diamond under a high temperature and high pressure. Traditional synthesis technics is assembling sheet of Ni70Mn25Co5 alloy accelerant and graphite by turn into a synthesizing cavity to synthesize. Diamond grows along the adjacent edge of graphite sheets with catalyst sheets. In recent years, the arisen technics of powder catalyst accelerates the promotion of conversion rate in diamond synthesizing.
In the article titled <Study on Catalyzing Efficiency of Sheet Catalyst or Powdery Catalyst used for Graphite Synthesizing Diamond> published by TANG Jingyou et al., it is disclosed that in using powder catalyst technics, the graphite powder and catalyst powder can be fully mixed. There is a bigger tangent area between the graphite power and catalyst powder. No long-distance pervasion is existed during graphite being synthesized as diamond. The transfer rate of graphite to diamond is increased greatly.
In same synthesis conditions, the yield of diamond by the powder catalyst is five times of that by the sheet catalyst.
In the article titled <New Technology and development of Chinese super hard materials> published by Fang Xiaohu, he said that “the particle size of both metal powder and graphite powder should be fine than 200 mesh, and mixing them by appropriate technics”, “a lower proportion between metal and graphite powder is suitable”, “In the synthesis process with powder catalyst, a metal film exist is necessary. If no metal film or the metal film is not complete, the diamond growth must be not good. The role of the metal film is for transferring carbon to the diamond nucleus and for accelerating diamond growth. In whole course, the crystal growth will stop when appearing an ill status or the crystal will grow incompletely. The powdery Catalyst easily forms a metal film. Moreover, the metal film and diamond nucleus are a kind of a monomer, which is an isolated, fine globular and omnidirectional globule. Its existence is so important that in case it has been formed and hold to the whole growth phase, the diamond is quite intact single crystal.”
The above-mentioned powder catalyst technics is based on mixing metal powder with graphite powder. As the big difference in density between metal powder and graphite powder, it is easy having segregate during mixing process. In addition, metal powders distributing in graphite is non-continuous. On the whole synthesizing cavity or appearance of single graphite particle, the environment is difficult to form a seriate metal film. It affects the growth of diamond crystals.